1. Field of the Invention
The present general inventive concept relates to a method and apparatus to efficiently transmit data and more particularly, to a method and apparatus to effectively aggregate data and transmit the data in a high-speed power line communication (PLC) network.
2. Description of the Related Art
When data is transmitted through a PLC network, data flows through a plurality of layers. FIG. 1 is a schematic diagram of a path along which data is transmitted through a plurality of layers in a PLC network.
Data transmitted by a transmitter connected to the PLC network arrives at an upper layer through a PHY layer (physical layer) and a media access control (MAC) layer, and then, conversely, the data is received by a data receiver again through the MAC layer and the PHY layer. In this process, the MAC layer receives the data transferred from one or more upper layers. However, in this case, data units of a variety of types and sizes may be transferred from one upper layer or from a plurality of upper layers. Here, the upper layers may include an Internet protocol (IP) stack of a transmission control protocol/user datagram protocol/Internet protocol (TCP/UDP/IP) or a non-IP stack. Here, a ‘data unit’ is a unit of data that is transferred through an interface from an upper layer, such as a transport (TS) packet.
In the conventional PLC network, a variety of applications (or a variety of data units) are transferred to the MAC layer from a plurality of upper layers, and thus interfaces corresponding to the respective applications also become increasingly diversified. Accordingly, the data units of the variety of types and sizes are transferred to the MAC layer through the variety of interfaces. Examples of the variety of interfaces include a direct TS interface, a universal serial bus (USB) interface, an IEEE 1394 interface, an IEEE 802.3 interface, a serial interface, and iso-asynchronous interface.
When the data units of the variety of types and sizes are transferred to the MAC layer, if the data units are transmitted individually, frequent overheads can occur. That is, if each of the data units transferred to the MAC layer from an upper layer or the PHY layer is transmitted individually in an individual frame, an ACK is individually generated in the frame corresponding to the data unit, thus causing an overhead. In addition, header information, padding information, and cyclic redundancy check (CRC) information for each layer in the frame corresponding to each data unit are generated, and these may also cause overheads. Accordingly, in order to minimize a transmission time required for the overheads, and to secure a better throughput even when an error occurs during transmission, it is necessary to effectively aggregate data units transferred to the MAC layer and transfer the aggregated data units at a time.
An effort has been made to aggregate an appropriate number of data units transferred to the MAC layer from upper layers and transfer the data units to a PHY layer.
FIG. 2 is a diagram illustrating a conventional method of aggregating a predetermined number of data units transferred to a MAC layer from upper layers and transferring the aggregated data units to a PHY layer.
However, as illustrated in FIG. 2, the conventional method considers only a case where data units transferred to the MAC layer from upper layers have an identical size. That is, according to the conventional method, data units having identical sizes transferred from upper layers are divided into frame blocks (FB) having the same size as that of the data unit, and a delimiter containing information on the frame block is combined with each frame block. Then, the frame blocks combined with the delimiters are aggregated to form one frame and this frame is transferred to a PHY layer.
For example, in a moving picture experts group (MPEG)-2 TS, only packets (data units) having identical sizes of 188 bytes are transferred from upper layers to a MAC layer. Accordingly, these packets can be divided into frame blocks of 188 bytes, the same size as that of the packets, and these frame blocks can be aggregated to form one frame and this frame can be transferred to a PHY layer.
However, this conventional method has the following problems.
First, when a variety of types and sizes of data units are transferred to a MAC layer, they cannot be efficiently aggregated and transmitted. That is, when the data units have a variety of sizes, one whole data unit may be included in one frame block, but two or more frame blocks may be needed for one data unit. That is, since a data unit is not the same size as a frame block, it is difficult for an idealistic case where one data unit corresponds to one frame block, to occur. Accordingly, after a data unit is inserted into a frame block, a remaining empty part exists in the frame block. In this empty part, another data unit may be inserted or it may be left empty. Accordingly, when a variety of types and sizes of data units are aggregated and transmitted at a time according to the conventional technology, complexity of implementation increases or implementation itself may become impossible.
Secondly, when a variety of types and sizes of data units are aggregated and transmitted at the same time according to the conventional technology, the boundary and size of each data unit included in the frame block, the number of data units included in the frame block, the number of each data unit included in the frame block, and other information as well as basic information, such as the number of the frame block and cyclic redundancy check (CRC) information should be included in the delimiter containing information on a frame block. Accordingly, the quantity of information that should be included in the delimiter increases substantially.
Thirdly, as the types of upper layers to which a data unit is to be transferred increase in order to increase types and sizes of data units, the processing in a MAC layer becomes more complicated.
Accordingly, the conventional method causes many problems when a variety of types and sizes of data units to be transferred from a variety of upper layers are to be effectively aggregated and transmitted.